SCRABBLE: Impute Single-Cell RNA-Seq Data Method

It aims to impute drop-out data by optimizing an objective function
that consists of three terms. The first term ensures that imputed values for
genes with nonzero expression remain as close to their original values as possible,
thus minimizing unwanted bias towards expressed genes. The second term ensures the
rank of the imputed data matrix to be as small as possible. The rationale is that
we only expect a limited number of distinct cell types in the samples. The third term
operates on the bulk RNA-Seq data. It ensures consistency between the average gene
expression of the aggregated imputed data and the average gene expression of the bulk
RNA-Seq data. We developed a convex optimization algorithm to minimize the objective function.